domingo, 6 de enero de 2013

"90% of Distant Galaxies in Universe Undetected"

The European Space Agency’s Herschel space telescope has discovered that previously unseen distant galaxies are responsible for a cosmic fog of infrared radiation.
The galaxies are some of the faintest and furthest objects seen by
Herschel, and open a new window on the birth of stars in the early
Universe. Astronomers estimate that there are billions and billions of
galaxies in the observable universe (as well as some seven trillion
dwarf galaxies). ESA astronomers say that for every ten far galaxies
observed, a hundred go undetected.

Astronomers realize that they may have underestimated the number of
galaxies in some parts of the universe by as much as 90 percent,
according to Matthew Hayes of the University of Geneva's Observatory,
who led the investigation using the world's most advanced optical
instrument -- Europe's Very Large Telescope
(VLT) in Chile, which has four 8.2-meter (26.65-feet) behemoths. They
turned two of the giants towards a well-studied area of deep space
called the GOODS-South field.

In the case of very distant, old galaxies, the telltale light may not
reach Earth as it is blocked by interstellar clouds of dust and gas --
and, as a result, these galaxies are missed by the map-makers.

"Astronomers
always knew they were missing some fraction of the galaxies... but for
the first time we now have a measurement. The number of missed galaxies
is substantial," said Matthew Hayes of the University of Geneva's
observatory, who led the investigation.

The team carried out two sets of observations in the same region,
hunting for light emitted by galaxies born 10 billion years ago.The
first looked for so-called Lyman-alpha
light, the classic telltale used to compile cosmic maps, named after
its U.S. discoverer, Theodore Lyman. Lyman-alpha is energy released by
excited hydrogen atoms. The second observation used a special camera
called HAWK-1 to look for a signature emitted at a different wavelength,
also by glowing hydrogen, which is known as the hydrogen-alpha (or
H-alpha) line.

The second sweep yielded a whole bagful of light sources that had not
been spotted using the Lyman-alpha technique. They include some of the
faintest galaxies ever found, forged at a time when the universe was
just an infant.

The astronomers conclude that Lyman-alpha surveys may only spot just a
tiny number of the total light emitted from far galaxies.
Astonishingly, as many as 90 percent of such distant galaxies may go
unseen in these exercises.

"If there are 10 galaxies seen, there could be a hundred there," said
Hayes. The discovery adds powerfully to knowledge about the timeline by
which stars and then galaxies formed.

The image at the top of the page shows the discovery of a previously
unresolved population of galaxies in the GOODS fields and the first
measurements of properties of galaxies in the almost unexplored
far-infrared domain are among the first exciting scientific results
achieved by Herschel's PACS and SPIRE instruments. These findings
confirm the extraordinary capabilities of ESA's new infrared space
observatory to investigate the formation and evolution of galaxies.